Nearly six months after the disastrous launch of Healthcare.gov, with the website running smoothly and more than five million people signed up as open enrollment heads to a close, a new glitch has come to light: Incorrect poverty-level guidelines are automatically telling what could be tens of thousands of eligible people they do not qualify for subsidized insurance.

The error in the federal marketplace primarily affects households with incomes just above the poverty line in states like Pennsylvania that have not expanded Medicaid. The mistake raises the price of their insurance by thousands of dollars, making insurance so unaffordable many may just give up and go without.

The error, which The Inquirer discovered while running scores of income scenarios through Healthcare.gov, again raises questions about the site’s accuracy that made daily headlines in early winter and that have cost President Obama considerable political capital.

It also highlights what some public policy experts say is a troubling lack of transparency in the marketplace’s eligibility determinations.

“It is almost impossible to work back from a decision and see what they did,” said Judy Solomon, vice president for health policy at the Center on Budget and Policy Priorities in Washington. Ideally, she said, a notice would say, “We have found that your income for 2014 will be X, and based on that income your tax credit will be Y.”

But the official determination letters simply state the amount of your tax credit and resulting insurance premium...